Publications

A simple approach to fabricate periodic arrays of ring bumps, disk and convex bumps or holes on silicon and gallium arsenide substrates is reported. In the process, a mono or double layer of 700 nm diameter silica colloidal particles were self-assembled on the substrates and a single pulse from a 200 fs laser at 387 nm wavelength was applied. The surfaces were irradiated at normal incidence by immersing the substrates in a glass container filled with acetone, carbon tetrachloride and 1,1,2-trichlor-trifluorethan liquid precursors. The influence of the medium on the near-field interactions for both substrates is investigated. (C) 2012 Elsevier B.V. All rights reserved.

The influence of different TiO2 precursors (laboratory-prepared sol-gel powders, dried and thermally treated at 400 degrees C, and commercial powders such as anatase by Aldrich and P25 Aeroxide by Evonik) on the structure and morphology of the titanate nanotubes obtained by hydrothermal method was investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. In all cases, titanate-based nanotubes were obtained, having similar structure and morphology. The effect of the thermal treatment on the structural stability was also studied by differential thermal analysis and thermogravimetry analysis (TG/DTA) and differetial scanning calorimetry (DSC) measurements up to 600 degrees C, to determine the transformation of titanate nanotubes into other phases. Complementarily, by XRD investigation, the phases that develop after the thermal treatment of the titanate nanotubes in 110-400 degrees C temperature range were identified. The TEM micrographs come to confirm the deterioration of morphology and transformation from nanotubes to particles. The thermal stability of the investigated nanotubes led to the conclusion that this property depends not only on the sodium content but also on the type of precursor. The highest thermal stability was noticed for the nanotubes synthesized starting with anatase (Aldrich) commercial powder.

Ferromagnetic FexGe1-x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 degrees C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 x 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe3 to approximately FeGe2, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane [110] easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

Composites based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and single-walled carbon nanotubes (SWNTs) were prepared by electrochemical polymerization of diphenylamine (DPA) on carbon nanotube films deposited onto Pt electrodes. HRTEM studies reveal that the electrochemical polymerization leads to the filling the spaces between tubes which compose the bundles, creating a monolithic film on the Pt electrode. The resulting composites were tested as active materials in supercapacitors. Resonant Raman scattering studies showed that the electropolymerization of DPA in the presence of H3PW12O40 and SWNTs leads to the covalent functionalization of SWNTs with doped PDPA. The covalent functionalization of SWNTs with PDPA doped with H3PW12O40 heteropolyanions was revealed by FTIR spectroscopy, based on the changes in the vibrational features of PDPA and H3PW12O40. These changes included i) a down-shift of the PDPA IR bands, which was attributed to the C-H bending vibrational mode of benzene (B), C-aromatic-N, C-C stretching (B) + C-H bending (B) and C-C stretching vibrations of the B ring, from 1174, 1321, 1495 and 1603 cm(-1) to 1165, 1313, 1487 and 1599 cm-1, respectively; ii) a change in the peak positions of IR bands associated with the W = O and P-O-W vibration modes of H3PW12O40; and iii) a down-shift of the IR band situated in the spectral range 650-725 cm(-1), which was assigned to the inter-ring deformation vibration mode. The characterization of symmetric solid-state supercapacitors was performed for electrodes prepared from i) SWNTs functionalized with PDPA doped with H3PW12O40 heteropolyanions, ii) SWNTs electrochemically decorated with H3PW12O40 heteropolyanions, and iii). PDPA doped with H3PW12O40 heteropolyanions. Preliminary results indicate high discharge capacitance values of up to 157.2 mF/cm(2) for SWNTs functionalized with PDPA doped with H3PW12O40 heteropolyanions. The discharge capacitance of this material is superior to those recorded for SWNTs electrochemically decorated with H3PW12O40 heteropolyanions (similar to 18.2 mF/cm(2)) and PDPA doped with H3PW12O40 heteropolyanions (similar to 62.1 mF/cm(2)). (c) 2012 Elsevier B.V. All rights reserved.

We have studied the one-step procedure for simultaneous synthesis and sintering of SiC-doped MgB2 by the spark plasma sintering technique. Two types of composition, one in which Mg is strongly deficient, with the atomic ratio , and one in which Mg content is slightly higher than the stoichiometric value, specifically , were investigated. The amount of SiC was 12 wt.% and 9 wt.%, respectively. For comparison we also studied the way the deficit of Mg can be compensated in a second process of sintering. The sample with Mg deficit shows that SiC is left almost unreacted but the results are spectacular: the highest critical temperature, 36.5 K, the highest upper critical field and the highest self-field critical current density 6.7x10(5) A/cm(2) at 10 K. In the sample with overstoichiometric Mg, SiC is decomposed, carbon diffuses within MgB2 but the critical temperature is only of 35.8 K and the zero-field critical current density is one order of magnitude lower. The compensation of the deficit of Mg in the two-step procedure is not efficient. The critical temperature is even lower, 35.8 K, the upper critical field is also lower despite SiC decomposition and C diffusion within MgB2 and the critical current density is slightly above 10(5) A/cm(2). However, at low temperatures and fields of order 7 T the sample with overstoichiometric Mg and the sample prepared by the two-step procedure have higher critical current density.

The influence of different ions NO3 (-) and SO4 (2-) on the carbon steel corrosion in ammonium chloride was investigated using mass loss measurements and potentiodynamic polarization. Corrosion products were analyzed using X-ray photoelectron spectroscopy (XPS) and simultaneous thermal and differential scanning calorimetry (TG/DSC). XPS analysis shows that the main product of corrosion is a non-stoichiometric Fe3+ oxyhydroxide, consisting of a mixture of FeO(OH) and FeO(OH) containing inclusions of these anions, species such as Fe3+O(OH,Cl-); Fe3+O(OH,SO4 (2-)); and Fe3+O(OH,NO3 (-)). TG/DSC confirms the decomposition of the rusty products formed by chemical corrosion, compounds like Fe3+ oxyhydroxides, with beta-FeOOH as the major phase, crystal structure of which may contain Cl-, NO3 (-), and SO4 (2-)-e.g., akaganeite [Fe3+O(OH,A)].

The Griess assay has been used to determine the possible changes in the measured NO2- concentrations induced by TiO2 nanoparticles in three types of nitrite-containing samples: aqueous NaNO2 solutions with known concentrations, and two types of cell culture media-Roswell Park Memorial Institute medium (RPMI-1640) and Dulbecco's Modified Eagle Medium (DMEM-F12) used either as delivered or enriched in NO2- by NaNO2 addition. We have used three types of titania with average particle sizes between 10 and 30 nm: Degussa P25 and two other samples (undoped and Fe3+-doped anatase TiO2) synthesised by a hydrothermal route in our laboratory. The structural, morphological, optical and physicochemical characteristics of the used materials have been studied by X-ray diffraction, transmission electron microscopy (EDX), Mossbauer spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption, UV-Vis reflectance spectroscopy, dynamic light scattering and diffuse reflectance infrared Fourier transform spectroscopy. The opacity and sedimentation behaviour of the studied TiO2 suspensions have been investigated by photometric attenuance measurements at 540 nm. To account for the photocatalytic properties of titania in a biologically relevant context, multiple Griess tests have been performed under controlled exposure to laboratory natural daylight illumination. The results show significant variations of light attenuance (associated with NO2- concentrations in the Griess test) depending on the opacity, sedimentation behaviour, NO2- adsorption and photocatalytic properties of the tested TiO2 nanomaterials. These findings identify material characteristics recommended to be considered when analysing the results of Griess tests performed in biological studies involving TiO2 nanoparticles.

Trace amounts of substitutional Mn2+ ions and shallow donors magnetic centers were identified by electron paramagnetic resonance (EPR) in crystalline Zn(OH)(2) prepared by precipitation of a Zn-nitrate solution with NaOH. Strong changes in the Mn2+ ions spectrum, as well as a sharp increase in the concentration of the shallow donor centers were observed by EPR in the 110-140 degrees C temperature range, during pulse annealing experiments in air up to 240 degrees C. They reflect the decomposition of the crystalline Zn(OH)(2) host lattice into nanocrystalline ZnO, confirmed by X-ray diffraction and thermal analysis measurements. Accurate spin Hamiltonian parameters of the observed paramagnetic centers were determined by lineshape simulation and fitting of the EPR spectra, to be used as reference data in further studies of nanocrystalline systems involving Zn(OH)(2). (C) 2012 Elsevier B.V. All rights reserved.

Due to the growing importance of low concentrated pollution of surface, ground and drinking, the photocatalytic decomposition of ibuprofen down to low ppm concentrations over titania catalyst has been investigated in detail. The catalyst was characterized by XRD, TEM, diffuse reflection UV-Vis and nitrogen adsorption measurement. The photocatalytic abatement of ibuprofen was monitored by UV-Vis spectrometry, chromatographic by GC/MS, and HPLC coupled electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Catalytic performance has been studied by varying the catalyst and substrate concentration as well as decreasing the catalyst-to-substrate mass ratio over a wide range. The photocatalytic treatment with titania catalyst leads to rapid mineralization of ibuprofen. Formation of intermediate reaction products has been investigated. It is proposed that intermediates in part form oligomeric species, which are responsible for catalyst poisoning. Additional, the influence of the pH value, oxygen supply and catalyst re-use have been checked. (C) 2012 Elsevier B.V. All rights reserved.

We report on the synthesis of novel ovine and bovine derived hydroxyapatite thin films on titanium substrates by pulsed laser deposition for a new generation of implants. The calcination treatment applied to produce the hydroxyapatite powders from ovine/bovine bones was intended to induce crystallization and to prohibit the transmission of diseases. The deposited films were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. Pull-off adherence and profilometry measurements were also carried out. X-ray diffraction ascertained the polycrystalline hydroxyapatite nature of the powders and films. Fourier transform infrared spectroscopy evidenced the vibrational bands characteristic to a hydroxyapatite material slightly carbonated. The micrographs of the films showed a uniform distribution of spheroidal particulates with a mean diameter of similar to 2 mu m. Pull-off measurements demonstrated excellent bonding strength values between the hydroxyapatite films and the titanium substrates. Because of their physical-chemical properties and low cost fabrication from renewable resources, we think that these new coating materials could be considered as a prospective competitor to synthetic hydroxyapatite used for implantology applications. (C) 2012 Elsevier B.V. All rights reserved.